Immunity to tumors

1. Tumor ImmunologyTumor Immunology
NCI, Cairo UniversityNCI, Cairo University

2. CancerCancer
IntroductionIntroduction
• Uncontrolled growth produces a tumor orUncontrolled growth produces a tumor or
neoplasm.neoplasm.
• A tumor that grows indefinitely and oftenA tumor that grows indefinitely and often
spreads (metastasis) is calledspreads (metastasis) is called malignantmalignant----
also called cancer.also called cancer.
• A tumor that is not capable of indefiniteA tumor that is not capable of indefinite
growth----growth----benignbenign..
• Malignant---kills host.Malignant---kills host.
• Benign---does not kill host.Benign---does not kill host.

3. Molecular Basis of Cancer
Uncontrolled
cell growth
Proto-oncogenes
Tumor-suppressor
genes
Mutations
Radiation
Chemical (Carcinogen)
Virus

4. Types of cancers based on etiologic agent
• Chemically-induced tumorsChemically-induced tumors
– Each tumor induced by a carcinogen (e.g. benzopyrene)Each tumor induced by a carcinogen (e.g. benzopyrene)
injected at various sites expresses a unique Ag.injected at various sites expresses a unique Ag.
– Thus difficult to develop vaccine.Thus difficult to develop vaccine.
• Virus-induced tumorsVirus-induced tumors
– Tumors induced by same virus express same tumor Ag.Tumors induced by same virus express same tumor Ag.
– Induce a strong immune response.Induce a strong immune response.
e.g. Gardasil vaccine – Human Papilloma Virus (HPV)e.g. Gardasil vaccine – Human Papilloma Virus (HPV)
induced cervical cancerinduced cervical cancer
• UV-induced tumorsUV-induced tumors
– UV radiation--->melanomasUV radiation--->melanomas
– Highly tumorigenicHighly tumorigenic

5. Evidence for the role of immune system in
tumor rejection
• Spontaneous regressionSpontaneous regression
• Infiltration of tumors by lymphocytes andInfiltration of tumors by lymphocytes and
macrophagesmacrophages
• Regression of metastases after removal of primaryRegression of metastases after removal of primary
tumortumor
• Regression after chemotherapyRegression after chemotherapy
• Lymphocyte proliferation in draining lymphLymphocyte proliferation in draining lymph
nodesnodes
• Higher incidence of cancer afterHigher incidence of cancer after
immunosuppression/immunodeficiency (AIDS,immunosuppression/immunodeficiency (AIDS,
neonates, aged, transplant patients)neonates, aged, transplant patients)

6. Syngeneic
(accepted)
Allogeneic
(rejected)
Inbred:
repeated
brother-
sister
matings
Outbred:
normal
population
Xenogeneic
(rejected)
Tumor Growth
Across Species
Rat
Mouse

7. Tumors stimulate specific, adaptive
immune responses
• Although tumor cells areAlthough tumor cells are
derived from host cells, thederived from host cells, the
tumors elicittumors elicit immune responsesimmune responses..
• They are surrounded byThey are surrounded by
mononuclear cell infiltratesmononuclear cell infiltrates
composed ofcomposed of T lymphocytesT lymphocytes,,
natural killer (NK) cellsnatural killer (NK) cells, and, and
macrophagesmacrophages..
• Activated lymphocytes andActivated lymphocytes and
macrophages are present inmacrophages are present in
lymph nodes draininglymph nodes draining..
• Lymphocytic infiltrates isLymphocytic infiltrates is
predictive of apredictive of a betterbetter prognosisprognosis..

8. • Tumors can induce protective immune responsesTumors can induce protective immune responses..
• A sarcoma induced in an inbred mouse by chemical carcinogenA sarcoma induced in an inbred mouse by chemical carcinogen
methylcholanthrene (MCA).methylcholanthrene (MCA).
• If tumor is excised and transplanted into other syngeneic mice, theIf tumor is excised and transplanted into other syngeneic mice, the
tumor grows.tumor grows.
• In contrastIn contrast, if the tumor is transplanted back into the original host, the, if the tumor is transplanted back into the original host, the
mousemouse rejectsrejects the tumor.the tumor.
• The same mouse that had become immune to its tumor is incapable ofThe same mouse that had become immune to its tumor is incapable of
rejecting MCA-induced tumors produced in other mice.rejecting MCA-induced tumors produced in other mice.
• Furthermore, T cells from the tumor-bearing animal can transferFurthermore, T cells from the tumor-bearing animal can transfer
protective immunity to the tumor to another tumor-free animal.protective immunity to the tumor to another tumor-free animal.
• Immune responses to tumors exhibit the defining characteristics ofImmune responses to tumors exhibit the defining characteristics of
adaptive immunityadaptive immunity, namely,, namely,
specificityspecificity,,
memorymemory,,
key role of T-key role of T- lymphocyteslymphocytes..

10. Immune responses frequently fail to prevent
the growth of tumors
• FirstFirst, tumor cells are derived from host cells and, tumor cells are derived from host cells and
resemble normal cells in many respects.resemble normal cells in many respects.
• Therefore, most tumors tend to beTherefore, most tumors tend to be weaklyweakly
immunogenicimmunogenic..
• Tumors that elicitTumors that elicit strong immune responsesstrong immune responses includeinclude
those induced by oncogenic viruses.those induced by oncogenic viruses.
• ManyMany spontaneous tumorsspontaneous tumors induce weak or eveninduce weak or even
undetectable immunityundetectable immunity..
• SecondSecond, the rapid growth and spread of tumors may, the rapid growth and spread of tumors may
overwhelm the capacity of the immune system.overwhelm the capacity of the immune system.
• ThirdThird, many tumors have specialized mechanisms for, many tumors have specialized mechanisms for
evading host immune responses.evading host immune responses.

11. Antigens expressed on tumor
cells
Major Histocompatability
Complex antigens
TST
A
TATA
TSTA: unique to a tumor
Play an important role in tumor rejection.
TATA: shared by normal and tumor cells
Tumor-associated developmental Ag (TADA)
Tumor-associated viral Ag (TAVA)
Tumor-specific
transplantation Ag
Tumor-associated
transplantation Ag

12. • It is important to identify tumor antigensIt is important to identify tumor antigens
in humans because:in humans because:
1- They may be used as1- They may be used as components ofcomponents of
tumor vaccines.tumor vaccines.
2- Antibodies and effector T cells2- Antibodies and effector T cells
generated against these antigens may begenerated against these antigens may be
used forused for immunotherapy.immunotherapy.

13. Identification of Tumor AntigensIdentification of Tumor Antigens
• The identification of many antigens expressedThe identification of many antigens expressed
by:by:
1- biochemical1- biochemical approachesapproaches
2- Molecular genetic approaches.2- Molecular genetic approaches.
• For tumor antigens recognized byFor tumor antigens recognized by CD8+CD8+
cytotoxiccytotoxic T lymphocytes (CTLs), cloned linesT lymphocytes (CTLs), cloned lines
ofof tumor-reactive CTLstumor-reactive CTLs from cancer patientsfrom cancer patients
are used as probes, to specifically identify theare used as probes, to specifically identify the
relevant peptide antigens or the genesrelevant peptide antigens or the genes
encoding the peptides.encoding the peptides.

14. • For example, manyFor example, many cloned CTLcloned CTL lineslines
specific for melanomas have been generatedspecific for melanomas have been generated
from thefrom the T cells of patientsT cells of patients..
• The T cells can be isolated from:The T cells can be isolated from:
- Peripheral blood- Peripheral blood..
- Lymph nodes draining the tumor.- Lymph nodes draining the tumor.
- directly from removed tumor tissue.- directly from removed tumor tissue.
• These T cells can be stimulated to grow inThese T cells can be stimulated to grow in
vitro byvitro by coculture with the tumor cellscoculture with the tumor cells, and, and
individual clones can be isolated.individual clones can be isolated.

15. • Because the T cells and the tumor are from theBecause the T cells and the tumor are from the
same individual, the major histocompatibilitysame individual, the major histocompatibility
complex (MHC) restriction of the T cells matchescomplex (MHC) restriction of the T cells matches
the MHC alleles expressed by the tumor.the MHC alleles expressed by the tumor.
• These tumor antigen–specific CTL clones have been usedThese tumor antigen–specific CTL clones have been used
to detect responses to tumor-derived peptides or responsesto detect responses to tumor-derived peptides or responses
to proteins made by complementary DNA (cDNA) librariesto proteins made by complementary DNA (cDNA) libraries
of the tumor.of the tumor.
• Such approaches were first used to identify humanSuch approaches were first used to identify human
melanoma antigensmelanoma antigens that stimulated CTL responses inthat stimulated CTL responses in
patients with melanoma.patients with melanoma.
• The same methods have been used to identify antigens thatThe same methods have been used to identify antigens that
are recognized by CD4+ helper cells, in which case theare recognized by CD4+ helper cells, in which case the
probes are helper T cell clones derived from patients’probes are helper T cell clones derived from patients’
CD4+ T cells.CD4+ T cells.

17. • A successful method forA successful method for identification ofidentification of
tumor antigenstumor antigens that have stimulated humoralthat have stimulated humoral
immune responses in tumor patients is calledimmune responses in tumor patients is called
the serologic analysis of recombinant cDNAthe serologic analysis of recombinant cDNA
expressionexpression (SEREX).(SEREX).
• In this method, expression libraries of cDNAIn this method, expression libraries of cDNA
derived from a patient’s tumor RNA arederived from a patient’s tumor RNA are
transfected into a cell line, and assays aretransfected into a cell line, and assays are
performed to detect binding of the cancerperformed to detect binding of the cancer
patient’s serum immunoglobulins to thepatient’s serum immunoglobulins to the
transfected cells.transfected cells.
• In this way,In this way, gene sequencesgene sequences for targetedfor targeted
proteins are obtained.proteins are obtained.

19. Products of Mutated Genes
• Oncogenes and mutated tumor suppressor genes produceOncogenes and mutated tumor suppressor genes produce
proteins that differ from normal cellular proteins and are,proteins that differ from normal cellular proteins and are,
therefore, recognized as tumor antigens.therefore, recognized as tumor antigens.
• Many tumorsMany tumors express genesexpress genes whose products arewhose products are
required forrequired for malignant transformationmalignant transformation or foror for
maintenance of the malignant phenotype.maintenance of the malignant phenotype.
• These genes are produced byThese genes are produced by point mutationspoint mutations,, deletionsdeletions,,
chromosomal translocationschromosomal translocations, or, or viral gene insertionsviral gene insertions
affecting cellular proto oncogenes or tumor suppressoraffecting cellular proto oncogenes or tumor suppressor
genes.genes.
• The products of these oncogenes and altered tumorThe products of these oncogenes and altered tumor
suppressor genes are synthesized in the cytoplasm of thesuppressor genes are synthesized in the cytoplasm of the
tumor cells and may enter thetumor cells and may enter the class I antigen-processingclass I antigen-processing
pathway.pathway.

20. • These proteins may enter theThese proteins may enter the class II antigen-processingclass II antigen-processing
pathway in antigen-presenting cells (APCs) that havepathway in antigen-presenting cells (APCs) that have
phagocytosed dead tumor cellsphagocytosed dead tumor cells..
• Because these altered genes are not present in normal cells,Because these altered genes are not present in normal cells,
peptides derived from them dopeptides derived from them do not induce self-tolerancenot induce self-tolerance
and mayand may stimulate T cell responsesstimulate T cell responses in the host.in the host.
• Some patients with cancer have circulating CD4+ andSome patients with cancer have circulating CD4+ and
CD8+ T cells that can respond to the products of mutatedCD8+ T cells that can respond to the products of mutated
oncogenes such asoncogenes such as Ras and Bcr/AblRas and Bcr/Abl proteins and mutatedproteins and mutated
tumor supressor genes such astumor supressor genes such as p53p53..
• In animals, immunization with mutated Ras or p53In animals, immunization with mutated Ras or p53
proteins induces CTLs and rejection responses againstproteins induces CTLs and rejection responses against
tumors expressing these mutants.tumors expressing these mutants.
• However, these proteins do not appear to be major targetsHowever, these proteins do not appear to be major targets
of tumor-specific CTLs in most patients with a variety ofof tumor-specific CTLs in most patients with a variety of
tumors.tumors.

21. • Tumor antigens may be produced by randomlyTumor antigens may be produced by randomly
mutated genes whose products are not related tomutated genes whose products are not related to
the malignant phenotypethe malignant phenotype..
• Tumor antigens that were defined by theTumor antigens that were defined by the
transplantation of carcinogen-inducedtransplantation of carcinogen-induced
tumors, calledtumors, called tumor-specific transplantationtumor-specific transplantation
antigensantigens,,
• They are mutants of various host cellularThey are mutants of various host cellular
proteins.proteins.
• Studies established that different rodentStudies established that different rodent
tumors, alltumors, all induced by the same carcinogeninduced by the same carcinogen,,
expressed different transplantation antigens.expressed different transplantation antigens.

22. • The tumor antigens identified by such experiments areThe tumor antigens identified by such experiments are
peptides derived frompeptides derived from mutated self proteinsmutated self proteins and presented inand presented in
the form of peptide–class I MHC complexes capable ofthe form of peptide–class I MHC complexes capable of
stimulating CTLsstimulating CTLs..
• These antigens are extremelyThese antigens are extremely diversediverse because the carcinogensbecause the carcinogens
that induce the tumors maythat induce the tumors may randomly mutagenizerandomly mutagenize any hostany host
gene, and the class I MHC antigen presenting pathway cangene, and the class I MHC antigen presenting pathway can
display peptides from any mutated cytosolic protein in eachdisplay peptides from any mutated cytosolic protein in each
tumor.tumor.
• Mutated cellular proteinsMutated cellular proteins are found more frequently inare found more frequently in
chemical carcinogenchemical carcinogen– or– or radiation-inducedradiation-induced animal tumorsanimal tumors
than in spontaneous human cancers, probably because theythan in spontaneous human cancers, probably because they
mutagenize many cellular genes.mutagenize many cellular genes.
• However, because of theHowever, because of the intrinsic genomic instabilityintrinsic genomic instability of manyof many
cancers, acancers, a wide variety of geneswide variety of genes may be mutated in tumormay be mutated in tumor
cells.cells.
• Even if these mutations do not contribute to the malignantEven if these mutations do not contribute to the malignant
phenotype, they may encode abnormal proteins that arephenotype, they may encode abnormal proteins that are
recognized by the immune systemrecognized by the immune system..

23. Abnormally Expressed but Unmutated Cellular ProteinsAbnormally Expressed but Unmutated Cellular Proteins
• Tumor antigens that elicit immune responsesTumor antigens that elicit immune responses
may be normal cellular proteins that aremay be normal cellular proteins that are
abnormally expressed in tumor cells.abnormally expressed in tumor cells.
• Many such antigens have been identified inMany such antigens have been identified in
human tumors, such as melanomas, by thehuman tumors, such as melanomas, by the
molecular cloningmolecular cloning of antigens that areof antigens that are
recognized by T cells and antibodies fromrecognized by T cells and antibodies from
tumor-bearing patientstumor-bearing patients..
• One of the surprises that emerged from theseOne of the surprises that emerged from these
studies was that some tumor antigens arestudies was that some tumor antigens are
normal proteinsnormal proteins that are producedthat are produced at lowat low
levels in normal cellslevels in normal cells and overexpressed inand overexpressed in
tumor cells .tumor cells .

24. • One such antigen isOne such antigen is tyrosinasetyrosinase, an enzyme, an enzyme
involved in melanin biosynthesis that isinvolved in melanin biosynthesis that is
expressed only inexpressed only in normal melanocytesnormal melanocytes andand
melanomasmelanomas..
• Both class I MHC–restricted CD8+ CTLBoth class I MHC–restricted CD8+ CTL
clones and class II MHC–restricted CD4+clones and class II MHC–restricted CD4+
helper T cell clones from melanomahelper T cell clones from melanoma
patientspatients recognize peptides derived fromrecognize peptides derived from
tyrosinase.tyrosinase.
• On face value, it is surprising that theseOn face value, it is surprising that these
patientspatients are able to respond to a normal selfare able to respond to a normal self
antigen.antigen.

25. • The likely explanation is that tyrosinase isThe likely explanation is that tyrosinase is
normallynormally produced in such small amountsproduced in such small amounts
and in so few cells that it is not recognizedand in so few cells that it is not recognized
by the immune system andby the immune system and fails to inducefails to induce
tolerance.tolerance.
• Therefore, the increased amount producedTherefore, the increased amount produced
by melanoma cells is able to elicit immuneby melanoma cells is able to elicit immune
responses.responses.
• The finding of tyrosinase-specific T cellThe finding of tyrosinase-specific T cell
responses in patientsresponses in patients raises the possibilityraises the possibility
that tyrosinase vaccinesthat tyrosinase vaccines may stimulate suchmay stimulate such
responses to melanomas.responses to melanomas.

26. • Cancer/testis antigens are proteins expressed in
gametes and trophoblasts and in many types of cancers
but not in normal somatic tissues.
• The first cancer/testis antigens were identified by
cloning genes from human melanomas that encoded
cellular protein antigens recognized by melanoma-
specific CTL clones derived from the melanoma-
bearing patients.
• These were called MAGE proteins, and they were
subsequently found to be expressed in other tumors in
addition to melanomas, including carcinomas of the
bladder, breast, skin, lung, and prostate and some
sarcomas, as well as in normal testes.

27. • Subsequent to identification of the MAGE
genes, several other unrelated gene families
have been identified that encode melanoma
antigens recognized by CTL clones derived
from melanoma patients.
• Like the MAGE proteins, these other
melanoma antigens are silent in most
normal tissues, except the testes or
trophoblasts in the placenta, but they are
expressed in a variety of malignant tumors.

28. • There are now more than 40 different cancer/testis
antigen families identified.
• Half are encoded by genes on the X chromosome
• The rest are encoded by genes distributed
throughout the genome.
• Although some cancer/testis antigens have been
shown to regulate transcription or translation of
other genes, the functions of most of these proteins
are unknown.
• In general, they are not required for the malignant
phenotype of the cells, and their sequences are
identical to the corresponding genes in normal cells;
that is, they are not mutated.
• Several X-linked cancer/testis antigens are currently
being used in tumor vaccine trials.

29. Antigens of Oncogenic Viruses
• The products of oncogenic viruses function as tumor antigens
and elicit specific T cell responses that may serve to eradicate
the tumors.
• DNA viruses are implicated in the development of a variety ofDNA viruses are implicated in the development of a variety of
tumors in humans and experimental animals.tumors in humans and experimental animals.
• Epstein-Barr virus (EBV).Epstein-Barr virus (EBV).
• Human papillomavirus (HPV).Human papillomavirus (HPV).
• Papovaviruses.Papovaviruses.
• In these DNA virus–induced tumors, virus-encoded proteinIn these DNA virus–induced tumors, virus-encoded protein
antigens are found in theantigens are found in the nucleusnucleus,, cytoplasmcytoplasm, or, or plasmaplasma
membranemembrane of the tumor cells.of the tumor cells.
• These endogenously synthesized proteins can be processed,These endogenously synthesized proteins can be processed,
and complexes of processed viral peptides with class I MHCand complexes of processed viral peptides with class I MHC
molecules may be expressed on the tumor cell surface.molecules may be expressed on the tumor cell surface.
• Because the viral peptides are foreign antigens, these tumorsBecause the viral peptides are foreign antigens, these tumors
are among theare among the most immunogenic tumors known.most immunogenic tumors known.

30. • The ability ofThe ability of adaptive immunityadaptive immunity to prevent theto prevent the
growth of DNA virus–induced tumors has beengrowth of DNA virus–induced tumors has been
established by many observations.established by many observations.
• These tumors are frequent inThese tumors are frequent in immunosuppressedimmunosuppressed::
• 1- Allograft recipients receiving1- Allograft recipients receiving immunosuppressiveimmunosuppressive
therapytherapy andand
• 2- Acquired immunodeficiency syndrome2- Acquired immunodeficiency syndrome (AIDS)(AIDS)..
• ExperimentsExperiments have shown that animals may behave shown that animals may be
specifically immunized against DNA virus–inducedspecifically immunized against DNA virus–induced
tumors and willtumors and will reject transplants of these tumors.reject transplants of these tumors.

31. • virus-encoded tumor antigens are notvirus-encoded tumor antigens are not
uniqueunique for each tumor but arefor each tumor but are shared by allshared by all
tumors induced by the same type of virustumors induced by the same type of virus..
• AA competent immune systemcompetent immune system plays a role inplays a role in
surveillance against virus-induced tumorssurveillance against virus-induced tumors
because of its ability to recognize andbecause of its ability to recognize and killkill
virus-infected cells.virus-infected cells.
• In fact, the concept ofIn fact, the concept of immune surveillanceimmune surveillance
against tumors is better established foragainst tumors is better established for
DNA virus–induced tumorsDNA virus–induced tumors than for anythan for any
other type of tumor.other type of tumor.

32. • The realization that immune responses against virusesThe realization that immune responses against viruses
protect individuals from virus-induced cancers has ledprotect individuals from virus-induced cancers has led
to the development ofto the development of vaccinesvaccines against oncogenicagainst oncogenic
viruses.viruses.
• AA vaccine against HPVvaccine against HPV is now in use, which has theis now in use, which has the
potential to reduce the incidence ofpotential to reduce the incidence of cervical cancercervical cancer..
• The vaccine is composed of recombinant HPVThe vaccine is composed of recombinant HPV capsidcapsid
proteinsproteins from the most common oncogenic strains offrom the most common oncogenic strains of
HPV, which formHPV, which form virus-like particles free of viralvirus-like particles free of viral
genome.genome.
• Vaccination againstVaccination against hepatitis B virushepatitis B virus is also reducingis also reducing
the incidence ofthe incidence of liver cancerliver cancer..
• The virus isThe virus is not oncogenicnot oncogenic, but it promotes the, but it promotes the
development of liver cancer by inducing chronicdevelopment of liver cancer by inducing chronic
inflammation (inflammation (risk factor for cancer development).risk factor for cancer development).

33. • RNA tumor virusesRNA tumor viruses (retroviruses) are important causes of(retroviruses) are important causes of
tumors in animals.tumors in animals.
• Retroviral oncogene products theoretically have the sameRetroviral oncogene products theoretically have the same
potential antigenic properties as mutated cellular oncogenes.potential antigenic properties as mutated cellular oncogenes.
• Humoral and cell mediated immune responses to retroviralHumoral and cell mediated immune responses to retroviral
gene products on tumor cells can be observed experimentally.gene products on tumor cells can be observed experimentally.
• The only well-defined human retrovirus that is known to causeThe only well-defined human retrovirus that is known to cause
tumors is human T cell lymphotropic virus 1 (HTLV-1), thetumors is human T cell lymphotropic virus 1 (HTLV-1), the
etiologic agent of adult T cell leukemia/lymphoma (ATL), aetiologic agent of adult T cell leukemia/lymphoma (ATL), a
malignant tumor of CD4+ T cells.malignant tumor of CD4+ T cells.
• AlthoughAlthough immune responses specific for HTLV-1–encodedimmune responses specific for HTLV-1–encoded
antigens have been demonstratedantigens have been demonstrated in individuals infected within individuals infected with
the virus,the virus, it is not clear whether they play any role init is not clear whether they play any role in
protective immunityprotective immunity against the development of tumors.against the development of tumors.
• Furthermore, patients with ATL are often profoundlyFurthermore, patients with ATL are often profoundly
immunosuppressed, probably because the virus infects CD4+ Timmunosuppressed, probably because the virus infects CD4+ T
cells and induces functional abnormalities in these cellscells and induces functional abnormalities in these cells.

34. Oncofetal Antigens
• Oncofetal antigens are proteins that are expressed at high levelsOncofetal antigens are proteins that are expressed at high levels
in cancer cells and in normal developing fetal but not adultin cancer cells and in normal developing fetal but not adult
tissues.tissues.
• The genes encoding these proteins areThe genes encoding these proteins are silenced duringsilenced during
developmentdevelopment andand derepressed with malignant transformationderepressed with malignant transformation..
• Oncofetal antigens are provideOncofetal antigens are provide markers that aid in tumormarkers that aid in tumor
diagnosis.diagnosis.
• It has become clear that their expression in adults isIt has become clear that their expression in adults is notnot
limited to tumorslimited to tumors..
• The proteins are increased in tissues and in the circulation inThe proteins are increased in tissues and in the circulation in
variousvarious inflammatory conditionsinflammatory conditions and are found in smalland are found in small
quantities even in normal tissues.quantities even in normal tissues.
• There isThere is no evidenceno evidence that oncofetal antigens are importantthat oncofetal antigens are important
inducers orinducers or targets of anti-tumor immunitytargets of anti-tumor immunity..

35. • CEA (CD66) is a highlyCEA (CD66) is a highly glycosylated membrane proteinglycosylated membrane protein
• Member of the immunoglobulin (Ig) superfamily.Member of the immunoglobulin (Ig) superfamily.
• Functions as an intercellular adhesion molecule.Functions as an intercellular adhesion molecule.
• CEA expression isCEA expression is normally highnormally high during theduring the first twofirst two
trimesterstrimesters of gestation in cells of the gut, pancreas, and liver.of gestation in cells of the gut, pancreas, and liver.
• Low expression is seen in normal adult colonic mucosa andLow expression is seen in normal adult colonic mucosa and
the lactating breast.the lactating breast.
• CEA expression isCEA expression is increasedincreased inin carcinomascarcinomas of the colon,of the colon,
pancreas, stomach, and breast, and serum levels arepancreas, stomach, and breast, and serum levels are
increased in these patients.increased in these patients.
• The level of serum CEA isThe level of serum CEA is used to monitor the persistence orused to monitor the persistence or
recurrence of the tumors after treatmentrecurrence of the tumors after treatment..
• CEA can also be elevated in the setting of non-neoplasticCEA can also be elevated in the setting of non-neoplastic
diseases, such asdiseases, such as chronic inflammatory conditions of thechronic inflammatory conditions of the
bowel or liver.bowel or liver.

36. • AFP is a circulatingAFP is a circulating glycoproteinglycoprotein normally synthesized andnormally synthesized and
secreted in fetal life by the yolk sac and liver.secreted in fetal life by the yolk sac and liver.
• FetalFetal serum concentrations can beserum concentrations can be as high as 2 to 3 mg/mLas high as 2 to 3 mg/mL,,
the protein isthe protein is replaced by albumin in adultreplaced by albumin in adult , and only low, and only low
levels are present in serum.levels are present in serum.
• Serum levels of AFP can be significantly elevated inSerum levels of AFP can be significantly elevated in
hepatocellular carcinoma, germ cell tumors, and, occasionally,hepatocellular carcinoma, germ cell tumors, and, occasionally,
gastric and pancreatic cancers.gastric and pancreatic cancers.
• An elevated serum AFP level is a useful indicator ofAn elevated serum AFP level is a useful indicator of advancedadvanced
liver or germ cell tumorsliver or germ cell tumors or of recurrence of these tumors.or of recurrence of these tumors.
• Detection of AFP in tissue sections byDetection of AFP in tissue sections by immunohistochemicalimmunohistochemical
techniquestechniques can help in the pathologic identification of tumorcan help in the pathologic identification of tumor
cells.cells.
• The diagnostic value of AFP as a tumor marker is limited byThe diagnostic value of AFP as a tumor marker is limited by
the fact that elevated serum levels are also found inthe fact that elevated serum levels are also found in non-non-
neoplastic diseases, such as cirrhosis of the liver.neoplastic diseases, such as cirrhosis of the liver.

37. Altered Glycolipid and Glycoprotein Antigens
• Tumors express higher than normal levels orTumors express higher than normal levels or abnormalabnormal
forms of surface glycoproteins and glycolipidsforms of surface glycoproteins and glycolipids, which may be, which may be
diagnostic markers and targets for therapy.diagnostic markers and targets for therapy.
• These altered molecules includeThese altered molecules include gangliosidesgangliosides,, blood groupblood group
antigensantigens, and, and mucinsmucins..
• Altered cell surface properties that result from abnormalAltered cell surface properties that result from abnormal
glycolipid and glycoprotein synthesis leads to tissue invasionglycolipid and glycoprotein synthesis leads to tissue invasion
and metastatic behavior.and metastatic behavior.
• ManyMany antibodiesantibodies have been raised in animals thathave been raised in animals that recognizerecognize
the carbohydrate groups or peptide cores of these moleculesthe carbohydrate groups or peptide cores of these molecules..
• Although most of the epitopes recognized by these antibodiesAlthough most of the epitopes recognized by these antibodies
are not specifically expressed on tumors, they are present atare not specifically expressed on tumors, they are present at
higher levels on cancer cells than on normal cells.higher levels on cancer cells than on normal cells.
• It is a target forIt is a target for cancer therapycancer therapy with specific antibodies.with specific antibodies.

38. • Gangliosides, including GM2, GD2, and GD3, areGangliosides, including GM2, GD2, and GD3, are
glycolipidsglycolipids expressed at high levels inexpressed at high levels in
neuroblastomas, melanomas, and many sarcomas.neuroblastomas, melanomas, and many sarcomas.
• They are anThey are an attractive target for tumor-specificattractive target for tumor-specific
therapiestherapies such as antibody therapy.such as antibody therapy.
• Clinical trials ofClinical trials of anti-ganglioside antibodiesanti-ganglioside antibodies andand
immunization withimmunization with ganglioside vaccinesganglioside vaccines are underare under
way in patients with melanoma.way in patients with melanoma.
• Mucins are high molecular- weight glycoproteinsMucins are high molecular- weight glycoproteins
containing numerous O-linked carbohydrate sidecontaining numerous O-linked carbohydrate side
chains on a core polypeptide.chains on a core polypeptide.
• Tumors often haveTumors often have dysregulated expressiondysregulated expression of theof the
enzymes that synthesize these carbohydrate sideenzymes that synthesize these carbohydrate side
chains, which leads to the appearance of tumor-chains, which leads to the appearance of tumor-
specific epitopes on the carbohydrate side chainsspecific epitopes on the carbohydrate side chains
or on the abnormally exposed polypeptide core.or on the abnormally exposed polypeptide core.

39. • Mucins includingMucins including CA-125 and CA-19-9CA-125 and CA-19-9, expressed on, expressed on
ovarian carcinomas, andovarian carcinomas, and MUC-1MUC-1, expressed on, expressed on
breast carcinomas.breast carcinomas.
• MUC-1 is anMUC-1 is an integral membrane proteinintegral membrane protein that isthat is
normally expressed only on the apical surface ofnormally expressed only on the apical surface of
breast ductal epithelium, abreast ductal epithelium, a site that is relativelysite that is relatively
sequestered from the immune system.sequestered from the immune system.
• In ductal carcinomas of the breast, however, theIn ductal carcinomas of the breast, however, the
molecule is expressed in an non polarized fashionmolecule is expressed in an non polarized fashion
and contains new, tumor-specific carbohydrate andand contains new, tumor-specific carbohydrate and
peptide epitopes detectable by mouse monoclonalpeptide epitopes detectable by mouse monoclonal
antibodies.antibodies.
• The peptide epitopes induceThe peptide epitopes induce both antibody and Tboth antibody and T cellcell
responses in cancer patients.responses in cancer patients.
• Efforts are under way to developEfforts are under way to develop vaccinesvaccines containingcontaining
immunogenic forms of MUC-1 epitopes.immunogenic forms of MUC-1 epitopes.

40. Tissue-Specific Differentiation AntigensTissue-Specific Differentiation Antigens
• Tumors may express molecules that areTumors may express molecules that are
present only on the normal cells of origin andpresent only on the normal cells of origin and
not on cells from other tissues.not on cells from other tissues.
• These antigens are called differentiationThese antigens are called differentiation
antigens because they areantigens because they are specificspecific forfor
particular lineages orparticular lineages or differentiation stagesdifferentiation stages
of various cell types.of various cell types.
• Their importance is as potentialTheir importance is as potential targets fortargets for
immunotherapyimmunotherapy and for identification ofand for identification of
the tissue of origin of tumors.the tissue of origin of tumors.

41. • For example, several melanoma antigens that are targets ofFor example, several melanoma antigens that are targets of
CTLs in patients are melanocyte differentiation antigens, suchCTLs in patients are melanocyte differentiation antigens, such
asas tyrosinasetyrosinase..
• CD10CD10 (previously called common acute lymphoblastic(previously called common acute lymphoblastic
leukemia antigen, or CALLA) andleukemia antigen, or CALLA) and CD20 inCD20 in Lymphomas.Lymphomas.
• Antibodies against these molecules are used for tumorAntibodies against these molecules are used for tumor
immunotherapy; the most successful immunotherapy for non-immunotherapy; the most successful immunotherapy for non-
Hodgkin’s B cell lymphomas is an anti-CD20 antibodyHodgkin’s B cell lymphomas is an anti-CD20 antibody
(rituximab).(rituximab).
• The idiotypic determinants of the surface Ig of a clonal B cellThe idiotypic determinants of the surface Ig of a clonal B cell
population are markers for that B cell clone because all otherpopulation are markers for that B cell clone because all other
B cells express different idiotypes.B cells express different idiotypes.
• Therefore, theTherefore, the Ig idiotypeIg idiotype is a highly specific tumor antigenis a highly specific tumor antigen
for B cell lymphomas and leukemias.for B cell lymphomas and leukemias.
• These differentiation antigens are normal self molecules, andThese differentiation antigens are normal self molecules, and
therefore theytherefore they do not usually induce strong immunedo not usually induce strong immune responsesresponses
in tumor bearing hosts.in tumor bearing hosts.

42. IMMUNE RESPONSES TO TUMORS
• The effector mechanisms of both innate andThe effector mechanisms of both innate and
adaptive immunity have been shown to killadaptive immunity have been shown to kill
tumor cells.tumor cells.
• Immunologists work on which of theseImmunologists work on which of these
mechanisms may contribute tomechanisms may contribute to
• 1-1- protection against tumorsprotection against tumors
• 2- to2- to enhanceenhance thesethese effector mechanisms ineffector mechanisms in
ways that are tumor specific.ways that are tumor specific.

43. Innate Immune Responses to
Tumors
• Some of the early research onSome of the early research on
functions of effector cells of thefunctions of effector cells of the
innate immune system, includinginnate immune system, including
NK cellsNK cells andand macrophagesmacrophages, focused, focused
on the ability of these cells to killon the ability of these cells to kill
cultured tumor cells.cultured tumor cells.

44. NKNK
• NK cells kill many types of tumor cells, especially cells thatNK cells kill many types of tumor cells, especially cells that
have reduced class I MHC expression and express ligands forhave reduced class I MHC expression and express ligands for
NK cell activating receptors.NK cell activating receptors.
• NK cells can killNK cells can kill virally infected cellsvirally infected cells and certainand certain tumor celltumor cell
lines.lines.
• NK cells also respond to the absence of class I MHCNK cells also respond to the absence of class I MHC
molecules because themolecules because the recognitionrecognition of class I MHC moleculesof class I MHC molecules
deliversdelivers inhibitory signals to NK cellsinhibitory signals to NK cells..
• Some tumors lose expression of class I MHC molecules thatSome tumors lose expression of class I MHC molecules that
makes the tumors good targets for NK cells.makes the tumors good targets for NK cells.
• Some tumors also expressSome tumors also express MIC-A, MIC-B, and ULBMIC-A, MIC-B, and ULB, which, which
are ligands for the NKG2D activating receptor on NK cells.are ligands for the NKG2D activating receptor on NK cells.
• In addition, NK cells can be targeted toIn addition, NK cells can be targeted to IgG antibody–IgG antibody–
coated tumor cells by Fc receptorscoated tumor cells by Fc receptors (FcγRIII or CD16).(FcγRIII or CD16).

45. • The tumoricidal capacity of NK cells is increased byThe tumoricidal capacity of NK cells is increased by
cytokines,cytokines, (IL-γ(IL-γ),), IL-15IL-15, and, and IL-12IL-12, with stimulation, with stimulation
of NK cell activity.of NK cell activity.
• IL-2–activated NK cells, called lymphokine-activatedIL-2–activated NK cells, called lymphokine-activated
killerkiller (LAK) cells(LAK) cells, are derived by culture of, are derived by culture of
peripheral bloodperipheral blood cells orcells or tumor infiltratingtumor infiltrating
lymphocyteslymphocytes from tumor patients with high doses offrom tumor patients with high doses of
IL-2.IL-2.
• These cells are more potent killers of tumors than areThese cells are more potent killers of tumors than are
un activated NK cells.un activated NK cells.
• T cell–deficient miceT cell–deficient mice do not have a high incidence ofdo not have a high incidence of
spontaneous tumors, and this is attributed to thespontaneous tumors, and this is attributed to the
presence ofpresence of normal numbers of NK cellsnormal numbers of NK cells that serve anthat serve an
immune surveillance function.immune surveillance function.
• Deficiencies of NK cells leads to an increasedDeficiencies of NK cells leads to an increased
incidence of EBV-associated lymphomas.incidence of EBV-associated lymphomas.

46. Macrophages
• Macrophages are capable of both inhibiting and promoting the growth andMacrophages are capable of both inhibiting and promoting the growth and
spread of cancers, depending on their activation state.spread of cancers, depending on their activation state.
• Classically activated M1 macrophages, display various anti-tumorClassically activated M1 macrophages, display various anti-tumor
functions.functions.
• Possible mechanisms include direct recognition of some surface antigensPossible mechanisms include direct recognition of some surface antigens
of tumor cells and activation of macrophages by IFN-γ produced byof tumor cells and activation of macrophages by IFN-γ produced by
tumor-specific T cells.tumor-specific T cells.
• M1M1 macrophages can kill tumor cells by the release of lysosomalmacrophages can kill tumor cells by the release of lysosomal
enzymes, reactive oxygen species, and nitric oxide.enzymes, reactive oxygen species, and nitric oxide.
• M1 macrophagesM1 macrophages also produce the cytokine tumor necrosis factoralso produce the cytokine tumor necrosis factor (TNF),(TNF),
which is as an agent that can kill tumors mainly by inducing thrombosiswhich is as an agent that can kill tumors mainly by inducing thrombosis
in tumor blood vessels.in tumor blood vessels.
• In contrast,In contrast, M2 macrophagesM2 macrophages may contribute to tumor progression.may contribute to tumor progression.
• These cells secrete vascular endothelial growth factor (VEGF),These cells secrete vascular endothelial growth factor (VEGF),
transforming growth factor-β (TGF-β), and other soluble factors thattransforming growth factor-β (TGF-β), and other soluble factors that
promote tumor angiogenesis.promote tumor angiogenesis.

47. Adaptive Immune Responses toAdaptive Immune Responses to
TumorsTumors
• Tumors elicit both T cell–mediated andTumors elicit both T cell–mediated and
humoral immune responses.humoral immune responses.
• T cells are the principal mediators ofT cells are the principal mediators of
antitumor immunity.antitumor immunity.
• This realization has led to considerableThis realization has led to considerable
efforts to enhance T cell responses for theefforts to enhance T cell responses for the
immunotherapy of cancers.immunotherapy of cancers.

48. T LymphocytesT Lymphocytes
• The principal mechanism of adaptive tumor immunity is killing of tumorThe principal mechanism of adaptive tumor immunity is killing of tumor
cells by CD8+ CTLs.cells by CD8+ CTLs.
• The ability of CTLs to provide effective anti-tumor immunity is seen inThe ability of CTLs to provide effective anti-tumor immunity is seen in
animal experimentsanimal experiments usingusing carcinogen inducedcarcinogen induced andand DNA virus–inducedDNA virus–induced
tumorstumors..
• CTLs may perform a surveillance function by recognizing and killingCTLs may perform a surveillance function by recognizing and killing
potentially malignant cells that express peptides which are derived frompotentially malignant cells that express peptides which are derived from
tumor antigens and are presented intumor antigens and are presented in association with class I MHCassociation with class I MHC
molecules.molecules.
• The role of immune surveillance in preventing common,The role of immune surveillance in preventing common, non virallynon virally
induced tumorsinduced tumors remainsremains controversialcontroversial because the frequency of suchbecause the frequency of such
tumors in T cell– deficient people is not clearly greater than the frequencytumors in T cell– deficient people is not clearly greater than the frequency
in immunocompetent individuals.in immunocompetent individuals.
• The prognosis of some types of human tumors is better when more CTLsThe prognosis of some types of human tumors is better when more CTLs
are present.are present.
• Mononuclear cells derived from the inflammatory infiltrate in human solidMononuclear cells derived from the inflammatory infiltrate in human solid
tumors, calledtumors, called tumor-infiltrating lymphocytes (TILs),tumor-infiltrating lymphocytes (TILs), contain CTLs withcontain CTLs with
the capacity to kill the tumor from which they were derived.the capacity to kill the tumor from which they were derived.

49. • CD8+ T cell responses specific for tumor antigensCD8+ T cell responses specific for tumor antigens
may require cross-presentation of the tumormay require cross-presentation of the tumor
antigens by dendritic cells.antigens by dendritic cells.
• Most tumor cells areMost tumor cells are not derived from APCsnot derived from APCs andand
dodo not express the costimulatorsnot express the costimulators needed to initiateneeded to initiate
T cell responses or the class II MHC moleculesT cell responses or the class II MHC molecules
needed toneeded to stimulate helper Tstimulate helper T cells that promote thecells that promote the
differentiation of CD8+ Tdifferentiation of CD8+ T cells.cells.
• Tumor cells or their antigens are ingested by hostTumor cells or their antigens are ingested by host
APCs, particularlyAPCs, particularly dendritic cellsdendritic cells, and tumor, and tumor
antigens are processedantigens are processed inside the APCsinside the APCs..
• Peptides derived from these antigens are thenPeptides derived from these antigens are then
displayed bound to class I MHC molecules fordisplayed bound to class I MHC molecules for
recognition by CD8+ T cells.recognition by CD8+ T cells.

50. Dendritic Cells
• Highly potent antigen processing andHighly potent antigen processing and
presenting cellspresenting cells
• Prime an Immune ResponsePrime an Immune Response
• Pulse with tumor Ags or gene transferPulse with tumor Ags or gene transfer
Cl II Cl I

51. • The APCs express costimulators that provide the signalsThe APCs express costimulators that provide the signals
needed for differentiation of CD8+ T cells into anti-tumorneeded for differentiation of CD8+ T cells into anti-tumor
CTLs, and the APCs express class II MHC molecules thatCTLs, and the APCs express class II MHC molecules that
may present internalized tumor antigens and activatemay present internalized tumor antigens and activate
CD4+ helper T cells as wellCD4+ helper T cells as well (cross-presentation).(cross-presentation).
• Once effector CTLs are generated, they are able toOnce effector CTLs are generated, they are able to
recognize and killrecognize and kill the tumor cells without a requirementthe tumor cells without a requirement
for costimulation.for costimulation.
• A practical application of the concept of cross-priming:A practical application of the concept of cross-priming:
1- Grow dendritic cells from a patient with cancer1- Grow dendritic cells from a patient with cancer,,
2- incubate the APCs with the cells or antigens from that2- incubate the APCs with the cells or antigens from that
patient’s tumor.patient’s tumor.
3- Use these antigen-pulsed APCs3- Use these antigen-pulsed APCs as vaccinesas vaccines to stimulateto stimulate
anti-tumor T cell responses.anti-tumor T cell responses.

52. Activation of naïve T cells
Signal I
Signal II
Effector T cells: killers
T cells
Tumor
Cross Presentation of
Tumor Antigens

55. • The importance of CD4+ helper T cells in tumorThe importance of CD4+ helper T cells in tumor
immunity isimmunity is less clearless clear..
• CD4+ cells may play a role in anti-tumor immuneCD4+ cells may play a role in anti-tumor immune
responses byresponses by providing cytokinesproviding cytokines for effective CTLfor effective CTL
development.development.
• Helper T cells specific for tumor antigens mayHelper T cells specific for tumor antigens may
secrete cytokinessecrete cytokines, such as, such as TNFTNF andand IFN-γIFN-γ, that can, that can
increase tumor cell class I MHC expression andincrease tumor cell class I MHC expression and
sensitivity to lysis by CTLs.sensitivity to lysis by CTLs.
• IFN-γIFN-γ may also activatemay also activate macrophagesmacrophages to kill tumorto kill tumor
cells.cells.
• Increased incidence of tumors in knockout miceIncreased incidence of tumors in knockout mice
lacking this cytokine, the IFN-γ receptorlacking this cytokine, the IFN-γ receptor, or, or
components of the IFN-γ receptor signaling cascade.components of the IFN-γ receptor signaling cascade.

56. AntibodiesAntibodies
• Tumor-bearing hosts may produce antibodies against variousTumor-bearing hosts may produce antibodies against various
tumor antigens.tumor antigens.
• Patients with EBV associated lymphomas have serumPatients with EBV associated lymphomas have serum
antibodies against EBV-encoded antigens expressed on theantibodies against EBV-encoded antigens expressed on the
surface of the lymphoma cells.surface of the lymphoma cells.
• Antibodies may kill tumor cells byAntibodies may kill tumor cells by
• 1- activating complement1- activating complement or byor by
• 2- antibody-dependent cell mediated cytotoxicity.2- antibody-dependent cell mediated cytotoxicity.
(Fc receptor–bearing MQ or NK cells mediate the killing).(Fc receptor–bearing MQ or NK cells mediate the killing).
• There isThere is little evidence for effective humoral immunelittle evidence for effective humoral immune
responses against tumorsresponses against tumors..
• Some effective therapeutic anti-tumor antibodies that areSome effective therapeutic anti-tumor antibodies that are
passively administered to patients work by ADCC.passively administered to patients work by ADCC.